Water resources

The Earth's oceans, land and atmosphere contain an estimated 1.4 × 106 km3 [1.4 × 1021 litres, or 1.4 billion billion tonnes] of water. The oceans contain 96.5% of the water, 2% is ice, and only 1% of global water is terrestrial, including the water in living organisms.

An 80m sea rise, resulting from most of the ice and snow melting into the oceans, would leave many countries looking a lot different

Water is cycled around the globe through terrestrial surface flow and evaporation/precipitation through the atmosphere. The terrestrial ecosystem makes use of the water as it cycles through, and, except for long-term aquifer storage, water is relatively temporary in its residence in soil, groundwater, rivers and lakes. Human societies are very dependent on water availability, and there are numerous accounts of failing civilisations, due to water shortages.

People have often intervened in the natural hydrological cycle, building dams, irrigation systems and mining water from underground. People have also drained wetlands and changed river and estuary courses in their quest to control their habitat.

With climate change, water is a major factor in the changing world environment. More energy in the oceans and atmosphere is changing the proportion of water locked in perpetual ice and snow, and causing more precipitation, and rising sea levels. Since human civilisation has generally developed along water highways, along coasts and rivers, changes to the world's water system is having serious repercussions on the human way of life.

Water Irregularities: Flood and Drought

Venice is a glimpse of the past and the future

The balance of water in any area is clearly an equation of input and output. Water can be retained by soil up to saturation point, and underground aquifers can transport water up to thousands of kilometres over thousands of years, making this resource effectively non-renewable.

Certain areas of the world receive too much precipitation, or are liable to river flooding due to their location. Unusually high rainfall in distant mountains is carried downstream through river systems, and, when the ground is saturated, the water table rises, causing rivers to overflow.

Other areas of the world are subject to prolonged droughts. Australia and California have been suffering some of the worst drought conditions in recorded history. To some degree, investment in infrastructure, such as water importation channels, irrigation schemes, and reservoir construction, can alleviate the intensity of the problem. However, where this infrastructure has been successful in the past has usually led to over-use, with salinization and contamination resulting. In addition, a burgeoning population may have grown up to be heavily dependent on imported water, which is not sustainable in the long-term, and a risky stratagem with a changing climate.

Water resource management aims to optimise the use of water, recognising that it is a valuable resource. In some cases, fresh water is only slowly renewable, and vulnerable to long-term contamination. Mankind uses water in ever-increasing amounts for sanitation, manufacturing, agriculture, and domestic consumption.

Water sources can often be transboundary, and large dams have created political antagonisms, and over-use and pollution have consequences beyond the economic area of exploitation.

Increasing Demands and Water Poverty

In 2007, the International Water Management Institute (located in Sri Lanka) carried out a survey of water availability for agricultural use (70% of water demand). 20% of the world's population experience regular or continuous water scarcity. Another 20% live in regions lacking sufficient funding to guarantee water demand: known as economic water scarcity.

Poor water quality is the greatest cause of world mortality and morbidity. Where wastewater can contaminate drinking water, and pathogens from sewerage can reach crops, bacteria, viruses, and parasitic worms can reach consumers. As a result, the developing world experiences high infant mortality through illnesses such as diarrhoea, and cholera outbreaks are common.

The loss of a free-flowing water supply in many areas has led to a 'solution' in the bottled water industry. However, replacing a once free commons good by an economic monetary good only extends the poverty generating dimension of poor water management.

Water Protection Conventions

Convention on the Protection and Use of Transboundary Watercourses and International Lakes (ECE Water Convention), Helsinki, 1992.

Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter (London Convention), London, 1972.

International Convention for the Prevention of Pollution from Ships, 1973, as modified by the Protocol of 1978 relating thereto (MARPOL 73/78), London 1973 and 1978.

International Convention for the Prevention of Pollution of the Sea by Oil, London 1954, 1962 and 1969.

United Nations Convention on the Law of the Sea LOS Convention, Montego Bay, 1982.

Convention for the Protection and Development of the Marine Environment and Coastal Region of the Mediterranean Sea Barcelona Convention, Barcelona, 1976.

Water Resources

Hydrological Cycle

The energy of the sun results in the atmosphere holding water. In the tropics this water can reach saturation. Any change in pressure or a fall in temperature will cause this water to precipitate. Water circulates due to the Earth's rotation and wind systems. When it precipitates over land, water enters the terrestrial water cycle. The latitude, altitude, and topography of the terrain determines whether the water returns rapidly to the sea in rivers or is stored temporarily or for long periods.

The Hydrosphere

The hydrosphere is a generic term for all the water on Earth. It includes underground water, mobile and immobile surface water, and atmospheric water. 2.5% of global water is not salinised, and is generally referred to as fresh water. Of this, 68.9% is locked up in frozen ice or snow.

Water Storage in the Hydrosphere

The hydrosphere is a generic term for all the water on Earth. It includes underground water, mobile and immobile surface water, and atmospheric water. 2.5% of global water is not salinised, and is generally referred to as fresh water. Of this, 68.9% is locked up in frozen ice or snow.

Here is a list of water storages in the hydrosphere, and their approximate retention (turnover) times - the time a molecule is likely to be retained before re-entering the hydrocycle in another phase.

Water storage

Retention time (years)

Polar ice caps

10k

Permafrost ice

10k

Oceans

2.5k

Groundwater

1.5k

Mountain glaciers

1.5k

Large lakes

17

Bogs (swamps)

5

Upper soil moisture

1

Atmospheric moisture

0.03

Rivers

0.04

Water Sustainability

Water is an essential part of life, and may be easily wasted or contaminated if poorly managed. It is also a breeding ground for disease and disease vectors, such as the mosquito. Diseases such as hepititus and cholera are transmitted through dirty water. Many parasites exist in water used by human populations.

Human industry uses a large amount of water, and can cause serious contamination of drinking and agricultural water through effluents of both organic and inorganic nature. Examples of these are heavy metals and sewerage emissions into rivers. Another major cause of water pollution is agriculture, which can cause large quantities of pesticides and fertilser to enter inland water resources. Excessive fertiliser leads to eutrophication, which is the occurrence of algal blooms on the surface of lakes and rivers, which rob the underwater ecosystem of light, and as a result oxygen due to lack of photosynthesis.

As the human population continues to grow, water has become a major limiting factor on development in many countries, in particular LEDCs (less economically developed countries), although some MEDCs (more economically developed countries), such as the USA and Australia, are experiencing water scarcity as a severely limiting factor in economic sustainability.

There is a huge discrepancy in use of water resources between countries, but it should be remembered that scarcity is a more meaningful measure of sustainability than consumption. One issue that needs addressing is the externalisation of rich countries' water problems by the exportation of water-intensive practices, such as manufacturing, to countries with water scarcity. An example of this is the advent of fastfood involving meat products in countries such as India, leading to resources, such as water and farmland, being inefficiently used. The amount of nutritional value in a hamburger makes it a poor use of resources compared to cereal crops.